Mak-Newts

On Tuesday, July 19, 2016 at 1:59:22 PM UTC-4, peterson wrote:
On Tue, 19 Jul 2016 10:56:27 -0700 (PDT), wsnell01 wrote:

On Tuesday, July 19, 2016 at 10:42:16 AM UTC-4, peterson wrote:
The
majority of higher quality telescopes are now being designed with
imaging in mind as the interest of amateur astronomers continues to
move away from visual observation.

Assertion made without evidence or proof. IOW, BAU.

Out of therapy again, I see.

Your libelous comment is proof that you just lost the argument, peterson.

On Tuesday, July 19, 2016 at 2:08:46 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 9:43:35 AM UTC-7, Chris L Peterson wrote:
On Tue, 19 Jul 2016 09:24:59 -0700 (PDT),
There's another factor, the cooled camera, longer the exposure more photons it collects.

Cooling reduces noise. But the noise level of the camera is
independent of the type of telescope. Regardless of camera, exposure
time is determined by aperture.

of course a larger diameter telescope OTA , has more resolution, also collects more photons!

In a few cases the relationship between aperture and resolution may be
important. But usually, resolution is determined by the atmosphere.
The higher resolution of a large aperture scope is usually more
apparent to visual observers, who can take advantage of fleeting
moments of excellent seeing in a way the imagers generally can't.

I've seen some images with SCT, because the large CO, the stars look very bloated.

No. A large CO does not produce bloated stars. It was either a scope
with poor optics, it was the result of poor collimation (very common
with SCTs), or some other factor.

Well, my C 11 SCT, does have a large airy disk around stars for sure!
More magnified the more it shows.
So, you don't think a camera would record that?

The Airy disk size is directly proportional to the focal ratio.

On Tuesday, July 19, 2016 at 11:16:10 AM UTC-7, wrote:
On Tuesday, July 19, 2016 at 2:08:46 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 9:43:35 AM UTC-7, Chris L Peterson wrote:
On Tue, 19 Jul 2016 09:24:59 -0700 (PDT),
There's another factor, the cooled camera, longer the exposure more photons it collects.

Cooling reduces noise. But the noise level of the camera is
independent of the type of telescope. Regardless of camera, exposure
time is determined by aperture.

of course a larger diameter telescope OTA , has more resolution, also collects more photons!

In a few cases the relationship between aperture and resolution may be
important. But usually, resolution is determined by the atmosphere.
The higher resolution of a large aperture scope is usually more
apparent to visual observers, who can take advantage of fleeting
moments of excellent seeing in a way the imagers generally can't.

I've seen some images with SCT, because the large CO, the stars look very bloated.

No. A large CO does not produce bloated stars. It was either a scope
with poor optics, it was the result of poor collimation (very common
with SCTs), or some other factor.

Well, my C 11 SCT, does have a large airy disk around stars for sure!
More magnified the more it shows.
So, you don't think a camera would record that?

The Airy disk size is directly proportional to the focal ratio.

No sht? How about the CO, ingenius?

On Tue, 19 Jul 2016 11:08:43 -0700 (PDT), StarDust
wrote:

I've seen some images with SCT, because the large CO, the stars look very bloated.

No. A large CO does not produce bloated stars. It was either a scope
with poor optics, it was the result of poor collimation (very common
with SCTs), or some other factor.

Well, my C 11 SCT, does have a large airy disk around stars for sure!
More magnified the more it shows.
So, you don't think a camera would record that?

The physical size of the Airy disk is determined by the focal ratio of
the telescope, and the resulting apparent size by the magnification
(or the pixel scale in the case of imaging). The central obstruction
doesn't change that. A large central obstruction does place a little
more energy into the outer rings, but it's unlikely that's really
going to make the stars look bigger (and it would certainly be very
subtle). When imaging, we almost never see diffraction rings around
stars at all, because seeing is the dominant factor in reducing
resolution.

Nearly all professional telescopes use RC optics these days, which
have very large obstructions. Resolution is not impacted, and for
imaging the effect on the MTF is generally very minor compared with
the other advantages of the design.

On Tuesday, July 19, 2016 at 2:21:19 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 11:16:10 AM UTC-7, wrote:
On Tuesday, July 19, 2016 at 2:08:46 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 9:43:35 AM UTC-7, Chris L Peterson wrote:
On Tue, 19 Jul 2016 09:24:59 -0700 (PDT),
There's another factor, the cooled camera, longer the exposure more photons it collects.

Cooling reduces noise. But the noise level of the camera is
independent of the type of telescope. Regardless of camera, exposure
time is determined by aperture.

of course a larger diameter telescope OTA , has more resolution, also collects more photons!

In a few cases the relationship between aperture and resolution may be
important. But usually, resolution is determined by the atmosphere.
The higher resolution of a large aperture scope is usually more
apparent to visual observers, who can take advantage of fleeting
moments of excellent seeing in a way the imagers generally can't.

I've seen some images with SCT, because the large CO, the stars look very bloated.

No. A large CO does not produce bloated stars. It was either a scope
with poor optics, it was the result of poor collimation (very common
with SCTs), or some other factor.

Well, my C 11 SCT, does have a large airy disk around stars for sure!
More magnified the more it shows.
So, you don't think a camera would record that?

The Airy disk size is directly proportional to the focal ratio.

No sht? How about the CO, ingenius?

You need to get on the winning side here, Stardust.

Among the worst effects of the CO is a reduction in resolution of low contrast detail, visually, since light is taken from the central area disk and moved to the rings.

On Tuesday, July 19, 2016 at 11:25:14 AM UTC-7, Chris L Peterson wrote:
On Tue, 19 Jul 2016 11:08:43 -0700 (PDT),
wrote:

I've seen some images with SCT, because the large CO, the stars look very bloated.

No. A large CO does not produce bloated stars. It was either a scope
with poor optics, it was the result of poor collimation (very common
with SCTs), or some other factor.

Well, my C 11 SCT, does have a large airy disk around stars for sure!
More magnified the more it shows.
So, you don't think a camera would record that?

The physical size of the Airy disk is determined by the focal ratio of
the telescope, and the resulting apparent size by the magnification
(or the pixel scale in the case of imaging). The central obstruction
doesn't change that. A large central obstruction does place a little
more energy into the outer rings, but it's unlikely that's really
going to make the stars look bigger (and it would certainly be very
subtle). When imaging, we almost never see diffraction rings around
stars at all, because seeing is the dominant factor in reducing
resolution.

Nearly all professional telescopes use RC optics these days, which
have very large obstructions. Resolution is not impacted, and for
imaging the effect on the MTF is generally very minor compared with
the other advantages of the design.

Well, in my 4" apo f/8.9 I have to look for any the airy disk, in my C-11 f/10 33% OC, pokes my eye out.
Maybe you should read Suiter's book, Star Testing Astronomical Telescopes !

On Tuesday, July 19, 2016 at 11:32:07 AM UTC-7, wrote:
On Tuesday, July 19, 2016 at 2:21:19 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 11:16:10 AM UTC-7, wrote:
On Tuesday, July 19, 2016 at 2:08:46 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 9:43:35 AM UTC-7, Chris L Peterson wrote:
On Tue, 19 Jul 2016 09:24:59 -0700 (PDT),
There's another factor, the cooled camera, longer the exposure more photons it collects.

Cooling reduces noise. But the noise level of the camera is
independent of the type of telescope. Regardless of camera, exposure
time is determined by aperture.

of course a larger diameter telescope OTA , has more resolution, also collects more photons!

In a few cases the relationship between aperture and resolution may be
important. But usually, resolution is determined by the atmosphere.
The higher resolution of a large aperture scope is usually more
apparent to visual observers, who can take advantage of fleeting
moments of excellent seeing in a way the imagers generally can't.

I've seen some images with SCT, because the large CO, the stars look very bloated.

No. A large CO does not produce bloated stars. It was either a scope
with poor optics, it was the result of poor collimation (very common
with SCTs), or some other factor.

Well, my C 11 SCT, does have a large airy disk around stars for sure!
More magnified the more it shows.
So, you don't think a camera would record that?

The Airy disk size is directly proportional to the focal ratio.

No sht? How about the CO, ingenius?

You need to get on the winning side here, Stardust.

Among the worst effects of the CO is a reduction in resolution of low contrast detail, visually, since light is taken from the central area disk and moved to the rings.

Yes, but more energy going into outer rings, shows up as a heavy ring around stars. At least, visually.
I see it all the time!

On Tuesday, July 19, 2016 at 2:33:21 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 11:25:14 AM UTC-7, Chris L Peterson wrote:
On Tue, 19 Jul 2016 11:08:43 -0700 (PDT),
wrote:

I've seen some images with SCT, because the large CO, the stars look very bloated.

No. A large CO does not produce bloated stars. It was either a scope
with poor optics, it was the result of poor collimation (very common
with SCTs), or some other factor.

Well, my C 11 SCT, does have a large airy disk around stars for sure!
More magnified the more it shows.
So, you don't think a camera would record that?

The physical size of the Airy disk is determined by the focal ratio of
the telescope, and the resulting apparent size by the magnification
(or the pixel scale in the case of imaging). The central obstruction
doesn't change that. A large central obstruction does place a little
more energy into the outer rings, but it's unlikely that's really
going to make the stars look bigger (and it would certainly be very
subtle). When imaging, we almost never see diffraction rings around
stars at all, because seeing is the dominant factor in reducing
resolution.

Nearly all professional telescopes use RC optics these days, which
have very large obstructions. Resolution is not impacted, and for
imaging the effect on the MTF is generally very minor compared with
the other advantages of the design.

Well, in my 4" apo f/8.9 I have to look for any the airy disk, in my C-11 f/10 33% OC, pokes my eye out.
Maybe you should read Suiter's book, Star Testing Astronomical Telescopes.

Then there must be something wrong with your larger scope, or else you are overlooking some other factor(s). Compare the scopes side-by-side on a night when both can perform at their best, use the same mag with each and control all possible variables. Then get back to us.

On Tuesday, July 19, 2016 at 11:25:01 AM UTC-5, StarDust wrote:
On Tuesday, July 19, 2016 at 8:50:45 AM UTC-7, Chris L Peterson wrote:
On Tue, 19 Jul 2016 08:46:21 -0700 (PDT), m
wrote:

For either, coma is a problem. Field curvature and most other off-axis
aberrations result in larger stars at the edges, which is preferable
to coma both aesthetically and scientifically.

Than, we should just stick to a high quality refractor, like the Takahashi 102!
http://www.lunar-captures.com//teles...sa102n_tar.jpg

Pinpoint sharp stars, down to the edge of the image!
http://3ainmfntxe31vi9qd1pxgpd1.wpen...l-1024x654.jpg

http://www.hendrenimaging.com/M22_8x...8_Crop_med.jpg

Met with a astro photographer on a star party, he was using a Tak-90 refractor on a Takahashi mount. He told me, with this set up, very light, portable, he can do up to 1.5 hrs of super accurate tracking. He dosn't like stacking images, so just take an images 1 time, 1 hr long or more, let the CCD collect all the photons, works perfect.

Certainly, high quality refractors generally offer the best
correction. With more surfaces to manipulate, very high orders of
correction are possible. But it comes at the cost of aperture. For
imagers, exposure time is controlled by aperture, and reduced exposure
time for a given target is usually seen as valuable.

There's another factor, the cooled camera, longer the exposure more photons it collects.
of course a larger diameter telescope OTA , has more resolution, also collects more photons! I've seen some images with SCT, because the large CO, the stars look very bloated.
He showed me on his laptop, some of the one shot DSO images he took with the Tak-90, it was very impassive and no processing.

Larger aperture = better signal/noise. In astrophotography the signal is usually very weak (except for a few of the brightest objects). Therefore the larger the aperture the better the signal will be. Some objects can be captured in 10 minute exposures, but some require many hours. In fact, it is not uncommon to have total exposure times of 40 hours or more (stacked of course).

Why stack several shorter images versus one long exposure? Sometimes the brightest parts of an object will reach saturation in a long exposure. therefore it is better to limit the exposure and stack many shorter ones, rather than burning out the bright parts in one long exposure.

Astrophotography is a complex subject. There is not one overall technique, nor is there one type of instrument to cover all bases. It can take years to master the art, but it is a fascinating thing to delve into if you have time and inclination.

On Tuesday, July 19, 2016 at 2:37:46 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 11:32:07 AM UTC-7, wrote:
On Tuesday, July 19, 2016 at 2:21:19 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 11:16:10 AM UTC-7, wrote:
On Tuesday, July 19, 2016 at 2:08:46 PM UTC-4, StarDust wrote:
On Tuesday, July 19, 2016 at 9:43:35 AM UTC-7, Chris L Peterson wrote:
On Tue, 19 Jul 2016 09:24:59 -0700 (PDT),
There's another factor, the cooled camera, longer the exposure more photons it collects.

Cooling reduces noise. But the noise level of the camera is
independent of the type of telescope. Regardless of camera, exposure
time is determined by aperture.

of course a larger diameter telescope OTA , has more resolution, also collects more photons!

In a few cases the relationship between aperture and resolution may be
important. But usually, resolution is determined by the atmosphere.
The higher resolution of a large aperture scope is usually more
apparent to visual observers, who can take advantage of fleeting
moments of excellent seeing in a way the imagers generally can't.

I've seen some images with SCT, because the large CO, the stars look very bloated.

No. A large CO does not produce bloated stars. It was either a scope
with poor optics, it was the result of poor collimation (very common
with SCTs), or some other factor.

Well, my C 11 SCT, does have a large airy disk around stars for sure!
More magnified the more it shows.
So, you don't think a camera would record that?

The Airy disk size is directly proportional to the focal ratio.

No sht? How about the CO, ingenius?

You need to get on the winning side here, Stardust.

Among the worst effects of the CO is a reduction in resolution of low contrast detail, visually, since light is taken from the central area disk and moved to the rings.

Yes, but more energy going into outer rings, shows up as a heavy ring around stars. At least, visually.
I see it all the time!

You should probably experiment by placing 33% obstructions in front of the refractor in order to get some good idea of an obstruction's effect on the Airy disk. Get back to us when you have some results.